Vyper is a statically typed language, which means that the type of each
variable (state and local) needs to be specified or at least known at
compile-time. Vyper provides several elementary types which can be combined
to form complex types.

In addition, types can interact with each other in expressions containing
operators.

Integer literals are interpreted as int128 by default. In cases where uint256 is more appropriate, such as assignment, the literal might be interpreted as uint256. Example: _variable:uint256=_literal. In order to explicitly cast a literal to a uint256 use convert(_literal,uint256).

Vyper allows the definition of types with discrete units e.g. meters, seconds, wei, … . These types may only be based on either uint256, int128 or decimal.
Vyper has 3 unit types built in, which are the following:

Mappings in Vyper can be seen as hash tables which are virtually initialized such that
every possible key exists and is mapped to a value whose byte-representation is
all zeros: a type’s default value. The similarity ends here, though: The key data is not actually stored
in a mapping, only its keccak256 hash used to look up the value. Because of this, mappings
do not have a length or a concept of a key or value being “set”.

It is possible to mark mappings public and have Vyper create a getter.
The _KeyType will become a required parameter for the getter and it will
return _ValueType.

Mapping types are declared as map(_KeyType,_ValueType).
Here _KeyType can be any base or bytes type. Mappings, contract or structs are not support as key types.
_ValueType can actually be any type, including mappings.

Example:

#Defining a mappingexampleMapping:map(int128,decimal)#Accessing a valueexampleMapping[0]=10.1

In Vyper, there is no null option like most programing languages have. Thus, every variable type has a default value. In order to check if a variable is empty, you will need to compare it to its type’s default value.
If you would like to reset a variable to its type’s default value, use the built-in clear() function.